This invention relates to a hardness tester which it makes possible to measure automatically hardness of specimens by using an image sensor.
The Vicker's hardness test is widely adopted as the typical one of the hardness tests for metallic material or the like. In the Vicker's test a load is applied slowly to the testing surface of specimen 2 using a quadrangular pyramid shaped diamond penetrator 1 (refer to FIG. 1a), having face to face angle .theta. = 136 degree thereof, and by this loading operation produces a dent 3 (hereafter called indentation) on the said surface, and the hardness value of the said specimen is defined as the quotient of the applied load divided by the surface area of the permanent indentation which remains after removing the load. That is, whereupon the applied load is P kg., and the diagonal length d mm of the said indentation 3 is measured, the Vicker's hardness HV can be indicated as follows: EQU HV= 2P/d.sup.2 sin 68.degree. = 1.854 P/d.sup.2 Kg/mm.sup.2
Among this Vicker's hardness test, a microvicker's tester or the like has been widely used in the past, and the measuring method thereof is that after giving a load to a specimen 2 by a diamond penetrator 1 of the loading mechanism of said tester and forming an indentation 3, the said diamond penetrator 1 is replaced with a measuring microscope using a resolver thereof without moving the specimen 2. Then, as shown in FIG. 2a, the diagonal edge points 3a, 3b of said indentation 3 formed on the specimen surface coincides with the edges of every reference lines 4a, 4b engraved on a resolver glass placed at the focal plane of the eyepiece in said microscope within the visual range thereof by the given operation and thus the diagonal length d of said indentation 3 is measured. But when the operator coincides the edges 3a, 3b of said indentation 3 with the edges of the every reference lines 4a, 4b within the visual range of said microscope, the coinciding position varies at every measuring operation due to the shape of said reference lines, the size of said indentation 3 and the physical condition of the operator.
Further, deviations appear at the coinciding positions of the edges of said reference lines 4a and 4b with edge points 3a and 3b of said indentation 3 due to personal error as shown in FIGS. 2b and 2c. If more than two operators measure the same indentation, the mutual difference appears naturally due to personal errors. As mentioned above, as for the Vicker's hardness tester due to such conventional visual measurement, the coinciding positions of the indentation edges 3a and 3b with the edges of the reference lines 4a and 4b could not be defined constant on account of the parallax of the operator himself or between the operators, or on account of the physical condition of the operator, therefore, therre have been defects which caused considerable amount of errors of the measured hardness value.